1. Field of the Invention
The present invention relates to a rotating electric machine with a brush, and more particularly to a rotating electric machine that is suitably employed for a brush motor for an electric power steering apparatus.
2. Background Art
A conventional commutator motor was composed of a housing having a through hole penetrated by a shaft and having a concave shape, an armature fixed to the shaft, a commutator fixed to an end portion of the shaft, a brush device comprising a base fixed to the housing by a clamp screw and having a tapped hole through which the clamp screw is inserted with a play, and a brush in contact with the commutator, and positioning means for positioning the brush to the commutator, the positioning means being provided between an outer circumferential face of the base and an inner wall face of the housing. Another conventional commutator motor was composed of a housing having a through hole penetrated by a shaft and having a concave shape, an armature fixed to the shaft, a commutator fixed to an end portion of the shaft, a brush device comprising a base fixed to the housing by a clamp screw and having a tapped hole through which the clamp screw is inserted with a play, with a plate contained by insert molding, and a brush in contact with the commutator, a grommet resiliently engaged in a cutout portion of the base, and the lead wires penetrating through the grommet and coupled with the plate electrically connected to the brush (e.g., refer to JP-A-2000-197314 (paragraphs [0004], [0008], FIG. 1, FIG. 9)).
Though in the conventional commutator motor, the positioning means was provided between the outer circumferential face of the base and the inner wall face of the housing to position the brush to the commutator, there was by necessity a small clearance for assembling between the outer circumferential face of the base and the inner wall face of the housing to accommodate the base in the inner wall face of the housing. Therefore, if the welding position of the lead wire to the joint portion was shifted, there was a problem that when the base and the grommet were inserted and assembled into the housing, the base or grommet was not smoothly assembled, the base was biased in a range of the small clearance to prevent smooth tightening of the clamp screw, or the brush sound was increased. Of course, in the apparatus without positioning means, the degree of the problem was significant. Also, in the apparatus having flexibility at the top end portion of the lead wire, it was required to change the lead wire to one having flexibility at the top end portion, resulting in a problem that the number of parts or working processes was increased, and the cost was increased.
Also, especially in the brush motor for electric power steering apparatus, since the armature is rotated in both directions, it is further required not only to reduce the brush sound, but also to make the brush sound low and uniform in both rotational directions to improve the silence within the vehicle, because if the magnitude of brush sound is varied depending on the rotational direction, the sound is very offensive to the ear.